This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
Various abbreviations that may appear in the description and drawings are defined as follows:                BW: bandwidth        ESD: electrostatic discharge        GSM: Global System for Mobile communications        HB: high band (generally >1 GHz)        LB: low band (generally <1 GHz)        RF: radio frequency        S-parameters: scattering parameters        S11: input reflection coefficient of Port 1        S22: input reflection coefficient of Port 2        SAR: specific absorption rate        SPST: single pole, single throw        Q: Quality factor        UMTS: Universal Mobile Telecommunications System        Z: complex input impedance        
Physically small antennas are utilized in modern portable electronic devices such as mobile phones. However, as the size of the antenna is reduced, it becomes more challenging to provide operation across a bandwidth that includes two or more separate, noncontiguous frequency bands of interest without incurring significant radiation losses. In general, decreasing the size of an antenna reduces the bandwidth and increases Q-value, which in turn decreases the number of possible frequency bands on which the antenna will operate with adequate radiation efficiency. For example, in order for a single antenna element to operate on the various frequency bands allocated to mobile phones in the US and Europe, the antenna and related matching circuitry needs to have wide bandwidth properties.
Conventionally, the use of matching components as well as radio frequency (RF) switches for switching additional ground connections in and out has enabled an increase in antenna bandwidth while maintaining adequate system radiation efficiency. However, as the antenna size is decreased below a certain level, the use of these conventional approaches is no longer adequate to achieve multiband operation across a plurality of noncontiguous frequency bands without incurring significant radiation losses.
The biological effects of RF radiation from mobile phones has been a subject of recent interest and study. Due to the fact that the antenna of a mobile device may be used in close proximity to the human body, antenna designs are required to take into consideration the rate at which RF energy radiated by the antenna is absorbed by the human body. This absorption is measured in terms of specific absorption rate (SAR) that indicates the amount of RF power absorbed per mass of tissue. Regardless of the size and configuration of an antenna design that is used for transmitting purposes, it is necessary to ensure that the combined SAR of a portable electronic device equipped with the antenna does not exceed the standards which have been promulgated by existing regulatory bodies. For example, in the United States, the Federal Communications Commission (FCC) requires that mobile phones have an SAR level at or below 1.6 watts per kilogram.